The plaintiffs brought an action in the Housing Court for Hampden County against the defendant, their landlord, seeking to recover damages and attorney’s fees for: (1) interference with quiet enjoyment and other violations of G. L. c. 186, § 14; (2) breach of the implied warranty of habitability; and (3) violations of G. L. c. 93A, § 2(a). The first two claims were heard and decided by a jury. The jury found for the plaintiffs on each of the claims and awarded actual damages of $982.50. A judge of the Housing Court decided the G. L. c. 93A claim. See Nei v. Burley, 388 Mass. 307, 311-315 (1983). The judge, in a written memorandum, “adopt[edj the findings of the jury. . . as to actual damages and [found] that conditions existed at the time of the inception of the tenancy which were in violation of the State Sanitary Code and of which the defendant was chargeable with notice . . . .” The judge further found that the defendant’s conduct in renting a substandard apartment violated G. L. c. 93A, § 2(a). He concluded, however, that the defendant’s conduct “was not a willful or knowing violation” of G. L. c. 93A but was “due to a misunderstanding as to the requirements] of the State Sanitary Code . . . .” Accordingly, the judge refused to multiply damages under the provision of G. L. c. 93A, § 9(3), inserted by St. 1986, c. 690, which authorizes recovery of “up to three but not less than two times [actual damages] if the court finds that [the unfair or deceptive act or practice] was a willful or knowing violation of . . . section two . . . .” The plaintiffs have appealed from the portion of the judgment which awards only single damages for the G. L. c. 93A violation.2